Axl is a receptor tyrosine kinase belonging to the Tyro3-Axl-Mer (TAM) receptor tyrosine kinase family whose ligand is a protein encoded by growth arrest-specific gene 6 (Gas6). The gene of this kinase was originally identified as a transforming gene in chronic myelogenous leukemia (Non Patent Document 1).
The Gas6/Axl signalling system has been reported to regulate diverse cellular responses such as cell survival, cell division, autophagy, cell migration, angiogenesis, platelet aggregation, and NK cell differentiation (Non Patent Document 2) Also, many reports show the overexpression of Axl in tissues of cancers such as primary colon cancer (Non Patent Document 3), gastric cancer (Non Patent Document 4), esophagus cancer (Non Patent Document 5), melanoma (Non Patent Document 6), ovary cancer (Non Patent Document 7), kidney cancer (Non Patent Document 8), endometrial cancer (Non Patent Document 9), and thyroid gland cancer (Non Patent Document 10). The presence of Axl has been found to be closely related to the lymph node involvement and stage of lung cancer and ER expression in breast cancer (Non Patent Document 11).
Axl has been further found to play a role in immunity (Non Patent Document 12), platelet functions (Non Patent Document 13), spermatogenesis (Non Patent Document 14), vascular calcification (Non Patent Document 15), thrombin-induced vascular smooth muscle cell (VSMC) proliferation (Non Patent Document 16), and various kidney diseases, for example, acute and chronic glomerulonephritis, diabetic nephropathy, and chronic allograft rejection (Non Patent Document 17). Axl inhibitors are expected to provide therapeutic benefits to many diseases including cancers (including solid tumors such as carcinoma and sarcoma, leukemia, and lymphoid malignant diseases) as well as vascular diseases (including, but not limited to, thrombosis, atherosclerosis, and restenosis), kidney diseases (including, but not limited to, acute and chronic glomerulonephritis, diabetic nephropathy, and graft rejection), and diseases in which the disorganized formation of blood vessels has serious consequences (including, but not limited to, diabetic retinopathy, retinopathy, psoriasis, rheumatoid arthritis, atheroma, Kaposi's sarcoma, and angioma).
Meanwhile, Mer, another member of the TAM receptor tyrosine kinase family to which Axl belongs, has been reported to cause autosomal recessive retinitis pigmentosa through its homozygous mutation (Non Patent Document 24). A certain mutation in Mer has been further reported to be related to childhood-onset rod-cone dystrophy (Non Patent Document 25).
Compounds having a sulfonamide structure (Patent Document 3), compounds having a pyrrolopyrimidine structure (Patent Documents 4 and 5), compounds having pyridine and pyrazine structures (Patent Document 6), compounds having a pyrazine structure (Patent Document 7), compounds having a pyrazinylbenzimidazole structure (Patent Document 8), compounds having an indolinone structure (Patent Document 9), compounds having triazolopyridine and triazolopyrimidine structures (Patent Document 10), compounds having an imidazole structure (Patent Document 11), compounds having a triazole structure (Patent Documents 12, 13, 14, 15, 16, 17, 20, 24, 25, 26, 27, and 28), compounds having a pyrimidinediamine structure (Patent Document 18), compounds having a pyrimidine structure (Patent Document 19 and Non Patent Documents 18 and 22), compounds having a quinolinyloxyphenylsulfonamide structure (Patent Document 21), compounds having a quinoline structure (Patent Documents 22 and 30 and Non Patent Document 21), compounds having a pyridine structure (Patent Documents 23 and 33 and Non Patent Document 19), compounds having an urea structure (Patent Document 29), compounds having a 2,4-disubstituted arylamide structure (Non Patent Document 20), compounds having a secosteroid structure (Non Patent Document 23), compounds having a bicyclic pyrimidine structure (Patent Documents 31, 32, and 34), and the like have been reported as compounds inhibiting Axl.